Even the shortest power failure in production can result in long downtimes and therefore high costs. If, for example, a plastic injection molding machine has come to a standstill, any unmelted granulate and plastic mass that has already melted and cooled down in the machine must first be completely removed before production can be restarted. It therefore makes sense to have a powerful system that can take over in the event of a power failure. With regard to the control system of a machine, a mains voltage fluctuation of just a few milliseconds can lead to problems and failure of the PLC and therefore the machine. It is therefore important to keep the control system stable and functional.

DC UPS instead of classic AC UPS

Industrial plant control systems usually run on a 24 V DC bus. It is therefore much more efficient to start here than on the AC side. AC UPS are complex systems and sometimes involve considerable additional losses due to the continuous conversion from alternating voltage (AC) to direct voltage (DC). If, on the other hand, buffering is only carried out on the DC side, there are only minor additional losses to keep the energy storage device charged with a regular mains supply: It is only converted from AC to DC once in the power supply unit and, in the event of a mains failure, the energy storage unit can supply the bus directly or via a simple DC/DC converter.

But which energy storage system is suitable for this type of DC UPS? First of all, classic rechargeable batteries, whether in lead, nickel metal hydride (NiMH) or lithium technology. Some of these can be coupled to the bus via diodes or ORing assemblies to compensate for voltage failures in the grid, as they only supply a slightly decreasing voltage from full charge to almost complete discharge. They can also bridge longer failures, but also take longer to reach full capacity again after a failure. They are ideal for shutting down the system in a controlled manner if the mains supply fails.

If, on the other hand, it is primarily a matter of intercepting brownouts or short blackouts, for example until another system steps in or the control system can quickly save its data, capacitors make more sense as energy storage devices. This is because they are all low-wear, deliver high power in the short term and can be fully recharged much faster than batteries. However, a DC/DC converter is required if a constant output voltage is needed, as the voltage of capacitors drops significantly as they discharge.

There are different UPS systems for these requirements, but both are suitable for snapping directly onto the top-hat rail in the control cabinet - including energy storage. A variant for direct installation in your own devices is also available. However, other individual solutions are also possible, including buffering large power supplies and local networks with a wide variety of energy storage systems.

DC UPS - all-in-one solution with accumulators

The 'DC-UPS' system from Adelsystem is a compact solution for 12, 24 and 48 V DIN rail systems with a current requirement of 3 to 35 A with a peak load capacity of up to three times the rated current. In addition to the actual UPS logic, these "all-in-one" solutions also contain a power supply unit and a battery charger. Back-up batteries with up to 7.2 Ah each can also be mounted on the top-hat rail. In this way, a completely fail-safe DIN rail power supply can be implemented in the same place instead of just a classic DIN rail power supply unit.

These all-in-one UPS are not intended to supply a complete production plant, but to keep individual control subsystems in operation even in the event of grid instability or failure. This eliminates the unnecessary detours of conventional UPSs, which first generate AC mains voltage from DC voltage. Another advantage: although a fault in the battery affects the UPS function, it does not lead to the output voltage being switched off if the input voltage is present, as is the case with an AC online UPS, for example. Finally, the charging current is dynamically controlled depending on the power requirement of the consumer: if the power drawn from the consumer is low, more is diverted to charge the battery.

The system is flexible and can work with lead and nickel-metal hydride batteries as well as lithium-ion batteries, charging, managing and controlling them. Deep discharge is prevented and charging is adapted to the current ambient and cell temperature. Reverse polarity, cell short circuits and increased internal resistance are also detected. Special battery care functions such as diagnostics and charging adapted to the temperature and internal resistance extend the life of the battery.

Fully equipped Adelsystem 'DC-UPS' with Modbus RTU can also be coupled with a control panel and web server for remote monitoring communication. This provides log functions, monitoring, alarm notification and numerous configuration options via RS485, SNMP and Ethernet TCP/IP. The wide-range input covers 115 and 230 VAC, and a three-phase version is already being planned.